Orthopedic implants, such as intramedullary nails, are implanted in bone tissue of a patient. Various methods and systems are known in the art for tracking the position of an orthopedic implant inside the patient body.
For example, U.S. Patent Application Publication 2004/0034355 describes method and apparatus for distal targeting of locking screws in intramedullary nails. A sensor, such as a wireless sensor, having a plurality of field transponders, is disposed in an orthopedic appliance, such as an intramedullary nail. The sensor is capable of detecting and discriminating the strength and direction of the different fields generated by the field generators.
U.S. Patent Application Publication 2008/0086145 describes a system that enables targeting of an instrument placed within a drill bushing aligns the axis of a drill bushing with the axis of a transverse hole in an intramedullary nail. The system includes a probe having an elongated member with a distal end, a magnet that is polarized along its longitudinal axis that is mounted perpendicularly to the distal end of the elongated member; and a processor executing programmed instructions to determine a position and orientation of the magnetic sensor array with respect to the targeting magnet.
U.S. Pat. No. 5,584,838 describes a femoral nail which has a transverse hole, and an arrangement for generating a magnetic field which has a maximum strength along an axis of the transverse hole and which decreases in strength in directions radially away from the axis.